The present invention relates to a driving device for an oscillatory actuator, including an oscillator, comprising a permanent magnet or an electromagnet, a stator comprising an electromagnet or a permanent magnet, and an elastic member that supports the oscillator. The present invention is particularly suited to use as a driving device for an oscillatory actuator for a vibrator used for a manner mode of a cellular phone.
To drive many of the vibrators used in a manner mode of conventional cellular phones eccentric motors are employed. Recently, however, attention has been paid to vibrators for cellular phones that employ a linearly oscillatory actuator without bearings, and which utilize resonance. U.S. Pat. No. 6,133,701 xe2x80x9cDRIVING CIRCUIT FOR OSCILLATORY ACTUATORxe2x80x9d describes a driving device in which a self-resonance frequency of a linearly oscillatory actuator is utilized to generate a driving signal. As shown in FIG. 13, this driving device is based on an analog method in which analog positive feedback is provided to a power amplifier to induce self-oscillation, thus driving a driving coil of the oscillatory actuator (referred to as a xe2x80x9cstator coilxe2x80x9d), in the neighborhood of the self-resonance frequency.
Further, Japanese Patent Laid-Open No. 8-331826 or 2001-128487 discloses a technique of pulling a driving frequency into a neighborhood of the resonance frequency of the oscillatory actuator. In this technique, however, an exclusive oscillation sensor needs to be provided separately from the driving coil.
The conventional driving device for the oscillatory actuator that causes self-oscillation (U.S. Pat. No. 6,133,701) requires a large capacitor that is difficult to integrate, and the device cannot properly maintain stable self-oscillation if the circuit actuator itself has a low quality factor Q. Further, a driving force increases very slowly when operation commences, thus requiring a long period of time in which to establish steady-state oscillation. Furthermore, the use of a square wave for a driving force results in low power efficiency.
In contrast to the prior art, the present invention does not require the use of a large capacitor, which hinder integration, and enables oscillation to continue even in a case that the actuator itself has a low quality factor Q. Further, the present invention allows driving force to rise quickly at the start of operation. Furthermore, in the present invention only a short time is required in which to establish steady-state oscillation; still further, since intermittent driving is employed, high power efficiency can be achieved.
The device that pulls the driving frequency into the neighborhood of the resonance point (Japanese Patent Laid-Open No. 8-331826) also controls a power supplied to a coil of a magnet on the basis of an output from a detecting means for detecting at least one of displacement, speed, and acceleration of a moving element. However, a drawback of this device is that it requires a sensing member used for detecting such components to be provided separately, which results in a complicated structure.
Further, Japanese Patent Laid-Open No. 2001-128487 discloses an oscillatory linear actuator for determining a frequency of a supplied current pulse on the basis of the result of detection of a natural oscillation of a spring oscillation system. However, using this technique, an amplitude value of the oscillation is detected as a physical quantity, and the frequency of a point with the largest amplitude value is set as driving frequency.
Further, claim 8 of Japanese Patent Laid-Open No. 2001-128487 describes an xe2x80x9coscillatory linear actuator (according to any one of claims 1 to 7), wherein a value for a natural frequency is determined in the absence of supply of a current to the coilxe2x80x9d. However, in this invention, the xe2x80x9cmeans for detecting the natural frequencyxe2x80x9d is also provided separately from the driving coil. As has been described, in the conventional art either a large capacitor or a large number of terminals for integration are required, which makes it impossible to provide an inexpensive integrated circuit for a driving circuit.
The present invention utilizes an electromotive force of a driving coil of an oscillatory actuator to detect a natural resonance frequency, thereby enabling an actuator having a simple and inexpensive structure to be provided.
In the present inventions, since a time ratio of polarities of an electromotive force is used to detect an electromotive force instead of an amplitude value, only two amplitude values, H and L (high, low) are required, thereby enabling a digital process to be utilized by means of a simple and inexpensive integrated circuit. Further, in the present invention a flyback pulse caused by residual inductance or the like, and which could adversely affect operation, has a high but narrow amplitude. Consequently, in the device of the present invention, no substantial adverse affects are caused by a flyback pulse. Further, in the present invention (as recited in claims 1-4), no external elements are required to realize the integrated circuit. Consequently, a number of terminals used in the integrated circuit can be significantly reduced.
As explained in the foregoing, the present invention solves the problems of the prior art by providing a driving device for an oscillatory actuator (as set forth in claim 1) that is able to detect an electromotive force of an oscillatory actuator, while a driving current for intermittent driving is interrupted. The oscillatory actuator is driven by using an FLL (Frequency Locked Loop) to control an oscillation frequency on the basis of a time ratio between positive and negative polarities of an electromotive force which depend on the deviation of the actuator from its self-resonance frequency. Accordingly, stable pulse driving can be maintained in a self-resonance frequency neighborhood specific to the oscillatory actuator.
Further, in the driving device of the present invention (as recited in claims 1 to 4), a digital FLL is employed, which enables almost all of its processes to be executed by a digital circuit.
The invention of claim 5 relates to a VCO (Voltage Controlled Oscillator) that is able continuously vary a frequency by using a low pass filter, to thereby remove alternating current components from a control signal. This oscillator uses an analog FLL as a control method but operates in substantially the same manner as the oscillator described above.
As stated, the present invention enables oscillation to be stably maintained regardless of the existence of a low quality factor Q. In fact, the present invention is characterized in that a relatively low Q has the effect of enlarging a frequency pull range, thus making it easier to absorb variations in the natural frequency of the oscillatory actuator.